/* ----------------------------------------------------------------------  
* Copyright (C) 2010 ARM Limited. All rights reserved.  
*  
* $Date:        29. November 2010  
* $Revision: 	V1.0.3  
*  
* Project: 	    CMSIS DSP Library  
* Title:		arm_correlate_fast_q15.c  
*  
* Description:	Fast Q15 Correlation.  
*  
* Target Processor: Cortex-M4/Cortex-M3
*  
* Version 1.0.3 2010/11/29 
*    Re-organized the CMSIS folders and updated documentation.  
*   
* Version 1.0.2 2010/11/11  
*    Documentation updated.   
*  
* Version 1.0.1 2010/10/05   
*    Production release and review comments incorporated.  
*  
* Version 1.0.0 2010/09/20   
*    Production release and review comments incorporated.  
* -------------------------------------------------------------------- */ 
 
#include "arm_math.h" 
 
/**  
 * @ingroup groupFilters  
 */ 
 
/**  
 * @addtogroup Corr  
 * @{  
 */ 
 
/**  
 * @brief Correlation of Q15 sequences (fast version).  
 * @param[in] *pSrcA points to the first input sequence.  
 * @param[in] srcALen length of the first input sequence.  
 * @param[in] *pSrcB points to the second input sequence.  
 * @param[in] srcBLen length of the second input sequence.  
 * @param[out] *pDst points to the location where the output result is written.  Length 2 * max(srcALen, srcBLen) - 1.  
 * @return none.  
 *  
 * <b>Scaling and Overflow Behavior:</b>  
 *  
 * \par  
 * This fast version uses a 32-bit accumulator with 2.30 format.  
 * The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit.  
 * There is no saturation on intermediate additions.  
 * Thus, if the accumulator overflows it wraps around and distorts the result.  
 * The input signals should be scaled down to avoid intermediate overflows.  
 * Scale down one of the inputs by 1/min(srcALen, srcBLen) to avoid overflow since a  
 * maximum of min(srcALen, srcBLen) number of additions is carried internally.  
 * The 2.30 accumulator is right shifted by 15 bits and then saturated to 1.15 format to yield the final result.  
 *  
 * \par  
 * See <code>arm_correlate_q15()</code> for a slower implementation of this function which uses a 64-bit accumulator to avoid wrap around distortion.  
 */ 
 
void arm_correlate_fast_q15( 
  q15_t * pSrcA, 
  uint32_t srcALen, 
  q15_t * pSrcB, 
  uint32_t srcBLen, 
  q15_t * pDst) 
{ 
  q15_t *pIn1;                                   /* inputA pointer               */ 
  q15_t *pIn2;                                   /* inputB pointer               */ 
  q15_t *pOut = pDst;                            /* output pointer               */ 
  q31_t sum, acc0, acc1, acc2, acc3;             /* Accumulators                  */ 
  q15_t *px;                                     /* Intermediate inputA pointer  */ 
  q15_t *py;                                     /* Intermediate inputB pointer  */ 
  q15_t *pSrc1;                                  /* Intermediate pointers        */ 
  q31_t x0, x1, x2, x3, c0;                      /* temporary variables for holding input and coefficient values */ 
  uint32_t j, k = 0u, count, blkCnt, outBlockSize, blockSize1, blockSize2, blockSize3;  /* loop counter                 */ 
  int32_t inc = 1;                               /* Destination address modifier */ 
  q31_t *pb;                                     /* 32 bit pointer for inputB buffer */ 
 
 
  /* The algorithm implementation is based on the lengths of the inputs. */ 
  /* srcB is always made to slide across srcA. */ 
  /* So srcBLen is always considered as shorter or equal to srcALen */ 
  /* But CORR(x, y) is reverse of CORR(y, x) */ 
  /* So, when srcBLen > srcALen, output pointer is made to point to the end of the output buffer */ 
  /* and the destination pointer modifier, inc is set to -1 */ 
  /* If srcALen > srcBLen, zero pad has to be done to srcB to make the two inputs of same length */ 
  /* But to improve the performance,  
   * we include zeroes in the output instead of zero padding either of the the inputs*/ 
  /* If srcALen > srcBLen,  
   * (srcALen - srcBLen) zeroes has to included in the starting of the output buffer */ 
  /* If srcALen < srcBLen,  
   * (srcALen - srcBLen) zeroes has to included in the ending of the output buffer */ 
  if(srcALen >= srcBLen) 
  { 
    /* Initialization of inputA pointer */ 
    pIn1 = (pSrcA); 
 
    /* Initialization of inputB pointer */ 
    pIn2 = (pSrcB); 
 
    /* Number of output samples is calculated */ 
    outBlockSize = (2u * srcALen) - 1u; 
 
    /* When srcALen > srcBLen, zero padding is done to srcB  
     * to make their lengths equal.  
     * Instead, (outBlockSize - (srcALen + srcBLen - 1))  
     * number of output samples are made zero */ 
    j = outBlockSize - (srcALen + (srcBLen - 1u)); 
 
    while(j > 0u) 
    { 
      /* Zero is stored in the destination buffer */ 
      *pOut++ = 0; 
 
      /* Decrement the loop counter */ 
      j--; 
    } 
 
  } 
  else 
  { 
    /* Initialization of inputA pointer */ 
    pIn1 = (pSrcB); 
 
    /* Initialization of inputB pointer */ 
    pIn2 = (pSrcA); 
 
    /* srcBLen is always considered as shorter or equal to srcALen */ 
    j = srcBLen; 
    srcBLen = srcALen; 
    srcALen = j; 
 
    /* CORR(x, y) = Reverse order(CORR(y, x)) */ 
    /* Hence set the destination pointer to point to the last output sample */ 
    pOut = pDst + ((srcALen + srcBLen) - 2u); 
 
    /* Destination address modifier is set to -1 */ 
    inc = -1; 
 
  } 
 
  /* The function is internally  
   * divided into three parts according to the number of multiplications that has to be  
   * taken place between inputA samples and inputB samples. In the first part of the  
   * algorithm, the multiplications increase by one for every iteration.  
   * In the second part of the algorithm, srcBLen number of multiplications are done.  
   * In the third part of the algorithm, the multiplications decrease by one  
   * for every iteration.*/ 
  /* The algorithm is implemented in three stages.  
   * The loop counters of each stage is initiated here. */ 
  blockSize1 = srcBLen - 1u; 
  blockSize2 = srcALen - (srcBLen - 1u); 
  blockSize3 = blockSize1; 
 
  /* --------------------------  
   * Initializations of stage1  
   * -------------------------*/ 
 
  /* sum = x[0] * y[srcBlen - 1]  
   * sum = x[0] * y[srcBlen - 2] + x[1] * y[srcBlen - 1]  
   * ....  
   * sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen - 1] * y[srcBLen - 1]  
   */ 
 
  /* In this stage the MAC operations are increased by 1 for every iteration.  
     The count variable holds the number of MAC operations performed */ 
  count = 1u; 
 
  /* Working pointer of inputA */ 
  px = pIn1; 
 
  /* Working pointer of inputB */ 
  pSrc1 = pIn2 + (srcBLen - 1u); 
  py = pSrc1; 
 
  /* ------------------------  
   * Stage1 process  
   * ----------------------*/ 
 
  /* The first loop starts here */ 
  while(blockSize1 > 0u) 
  { 
    /* Accumulator is made zero for every iteration */ 
    sum = 0; 
 
    /* Apply loop unrolling and compute 4 MACs simultaneously. */ 
    k = count >> 2; 
 
    /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.  
     ** a second loop below computes MACs for the remaining 1 to 3 samples. */ 
    while(k > 0u) 
    { 
      /* x[0] * y[srcBLen - 4] , x[1] * y[srcBLen - 3] */ 
      sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum); 
      /* x[3] * y[srcBLen - 1] , x[2] * y[srcBLen - 2] */ 
      sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum); 
 
      /* Decrement the loop counter */ 
      k--; 
    } 
 
    /* If the count is not a multiple of 4, compute any remaining MACs here.  
     ** No loop unrolling is used. */ 
    k = count % 0x4u; 
 
    while(k > 0u) 
    { 
      /* Perform the multiply-accumulates */ 
      /* x[0] * y[srcBLen - 1] */ 
      sum = __SMLAD(*px++, *py++, sum); 
 
      /* Decrement the loop counter */ 
      k--; 
    } 
 
    /* Store the result in the accumulator in the destination buffer. */ 
    *pOut = (q15_t) (sum >> 15); 
    /* Destination pointer is updated according to the address modifier, inc */ 
    pOut += inc; 
 
    /* Update the inputA and inputB pointers for next MAC calculation */ 
    py = pSrc1 - count; 
    px = pIn1; 
 
    /* Increment the MAC count */ 
    count++; 
 
    /* Decrement the loop counter */ 
    blockSize1--; 
  } 
 
  /* --------------------------  
   * Initializations of stage2  
   * ------------------------*/ 
 
  /* sum = x[0] * y[0] + x[1] * y[1] +...+ x[srcBLen-1] * y[srcBLen-1]  
   * sum = x[1] * y[0] + x[2] * y[1] +...+ x[srcBLen] * y[srcBLen-1]  
   * ....  
   * sum = x[srcALen-srcBLen-2] * y[0] + x[srcALen-srcBLen-1] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]  
   */ 
 
  /* Working pointer of inputA */ 
  px = pIn1; 
 
  /* Working pointer of inputB */ 
  py = pIn2; 
 
  /* Initialize inputB pointer of type q31 */ 
  pb = (q31_t *) (py); 
 
  /* count is index by which the pointer pIn1 to be incremented */ 
  count = 0u; 
 
  /* -------------------  
   * Stage2 process  
   * ------------------*/ 
 
  /* Stage2 depends on srcBLen as in this stage srcBLen number of MACS are performed.  
   * So, to loop unroll over blockSize2,  
   * srcBLen should be greater than or equal to 4, to loop unroll the srcBLen loop */ 
  if(srcBLen >= 4u) 
  { 
    /* Loop unroll over blockSize2, by 4 */ 
    blkCnt = blockSize2 >> 2u; 
 
    while(blkCnt > 0u) 
    { 
      /* Set all accumulators to zero */ 
      acc0 = 0; 
      acc1 = 0; 
      acc2 = 0; 
      acc3 = 0; 
 
      /* read x[0], x[1] samples */ 
      x0 = *(q31_t *) (px++); 
      /* read x[1], x[2] samples */ 
      x1 = *(q31_t *) (px++); 
 
      /* Apply loop unrolling and compute 4 MACs simultaneously. */ 
      k = srcBLen >> 2u; 
 
      /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.  
       ** a second loop below computes MACs for the remaining 1 to 3 samples. */ 
      do 
      { 
        /* Read the first two inputB samples using SIMD:  
         * y[0] and y[1] */ 
        c0 = *(pb++); 
 
        /* acc0 +=  x[0] * y[0] + x[1] * y[1] */ 
        acc0 = __SMLAD(x0, c0, acc0); 
 
        /* acc1 +=  x[1] * y[0] + x[2] * y[1] */ 
        acc1 = __SMLAD(x1, c0, acc1); 
 
        /* Read x[2], x[3] */ 
        x2 = *(q31_t *) (px++); 
 
        /* Read x[3], x[4] */ 
        x3 = *(q31_t *) (px++); 
 
        /* acc2 +=  x[2] * y[0] + x[3] * y[1] */ 
        acc2 = __SMLAD(x2, c0, acc2); 
 
        /* acc3 +=  x[3] * y[0] + x[4] * y[1] */ 
        acc3 = __SMLAD(x3, c0, acc3); 
 
        /* Read y[2] and y[3] */ 
        c0 = *(pb++); 
 
        /* acc0 +=  x[2] * y[2] + x[3] * y[3] */ 
        acc0 = __SMLAD(x2, c0, acc0); 
 
        /* acc1 +=  x[3] * y[2] + x[4] * y[3] */ 
        acc1 = __SMLAD(x3, c0, acc1); 
 
        /* Read x[4], x[5] */ 
        x0 = *(q31_t *) (px++); 
 
        /* Read x[5], x[6] */ 
        x1 = *(q31_t *) (px++); 
 
        /* acc2 +=  x[4] * y[2] + x[5] * y[3] */ 
        acc2 = __SMLAD(x0, c0, acc2); 
 
        /* acc3 +=  x[5] * y[2] + x[6] * y[3] */ 
        acc3 = __SMLAD(x1, c0, acc3); 
 
      } while(--k); 
 
      /* For the next MAC operations, SIMD is not used  
       * So, the 16 bit pointer if inputB, py is updated */ 
      py = (q15_t *) (pb); 
 
      /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.  
       ** No loop unrolling is used. */ 
      k = srcBLen % 0x4u; 
 
      if(k == 1u) 
      { 
        /* Read y[4] */ 
        c0 = *py; 
        c0 = c0 & 0x0000FFFF; 
 
        /* Read x[7] */ 
        x3 = *(q31_t *) px++; 
 
        /* Perform the multiply-accumulates */ 
        acc0 = __SMLAD(x0, c0, acc0); 
        acc1 = __SMLAD(x1, c0, acc1); 
        acc2 = __SMLADX(x1, c0, acc2); 
        acc3 = __SMLADX(x3, c0, acc3); 
      } 
 
      if(k == 2u) 
      { 
        /* Read y[4], y[5] */ 
        c0 = *(pb); 
 
        /* Read x[7], x[8] */ 
        x3 = *(q31_t *) px++; 
 
        /* Read x[9] */ 
        x2 = *(q31_t *) px++; 
 
        /* Perform the multiply-accumulates */ 
        acc0 = __SMLAD(x0, c0, acc0); 
        acc1 = __SMLAD(x1, c0, acc1); 
        acc2 = __SMLAD(x3, c0, acc2); 
        acc3 = __SMLAD(x2, c0, acc3); 
      } 
 
      if(k == 3u) 
      { 
        /* Read y[4], y[5] */ 
        c0 = *pb++; 
 
        /* Read x[7], x[8] */ 
        x3 = *(q31_t *) px++; 
 
        /* Read x[9] */ 
        x2 = *(q31_t *) px++; 
 
        /* Perform the multiply-accumulates */ 
        acc0 = __SMLAD(x0, c0, acc0); 
        acc1 = __SMLAD(x1, c0, acc1); 
        acc2 = __SMLAD(x3, c0, acc2); 
        acc3 = __SMLAD(x2, c0, acc3); 
 
        /* Read y[6] */ 
        c0 = (q15_t) (*pb); 
        c0 = c0 & 0x0000FFFF; 
 
        /* Read x[10] */ 
        x3 = *(q31_t *) px++; 
 
        /* Perform the multiply-accumulates */ 
        acc0 = __SMLADX(x1, c0, acc0); 
        acc1 = __SMLAD(x2, c0, acc1); 
        acc2 = __SMLADX(x2, c0, acc2); 
        acc3 = __SMLADX(x3, c0, acc3); 
      } 
 
      /* Store the result in the accumulator in the destination buffer. */ 
      *pOut = (q15_t) (acc0 >> 15); 
      /* Destination pointer is updated according to the address modifier, inc */ 
      pOut += inc; 
 
      *pOut = (q15_t) (acc1 >> 15); 
      pOut += inc; 
 
      *pOut = (q15_t) (acc2 >> 15); 
      pOut += inc; 
 
      *pOut = (q15_t) (acc3 >> 15); 
      pOut += inc; 
 
      /* Increment the pointer pIn1 index, count by 1 */ 
      count += 4u; 
 
      /* Update the inputA and inputB pointers for next MAC calculation */ 
      px = pIn1 + count; 
      py = pIn2; 
      pb = (q31_t *) (py); 
 
 
      /* Decrement the loop counter */ 
      blkCnt--; 
    } 
 
    /* If the blockSize2 is not a multiple of 4, compute any remaining output samples here.  
     ** No loop unrolling is used. */ 
    blkCnt = blockSize2 % 0x4u; 
 
    while(blkCnt > 0u) 
    { 
      /* Accumulator is made zero for every iteration */ 
      sum = 0; 
 
      /* Apply loop unrolling and compute 4 MACs simultaneously. */ 
      k = srcBLen >> 2u; 
 
      /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.  
       ** a second loop below computes MACs for the remaining 1 to 3 samples. */ 
      while(k > 0u) 
      { 
        /* Perform the multiply-accumulates */ 
        sum += ((q31_t) * px++ * *py++); 
        sum += ((q31_t) * px++ * *py++); 
        sum += ((q31_t) * px++ * *py++); 
        sum += ((q31_t) * px++ * *py++); 
 
        /* Decrement the loop counter */ 
        k--; 
      } 
 
      /* If the srcBLen is not a multiple of 4, compute any remaining MACs here.  
       ** No loop unrolling is used. */ 
      k = srcBLen % 0x4u; 
 
      while(k > 0u) 
      { 
        /* Perform the multiply-accumulates */ 
        sum += ((q31_t) * px++ * *py++); 
 
        /* Decrement the loop counter */ 
        k--; 
      } 
 
      /* Store the result in the accumulator in the destination buffer. */ 
      *pOut = (q15_t) (sum >> 15); 
      /* Destination pointer is updated according to the address modifier, inc */ 
      pOut += inc; 
 
      /* Increment the pointer pIn1 index, count by 1 */ 
      count++; 
 
      /* Update the inputA and inputB pointers for next MAC calculation */ 
      px = pIn1 + count; 
      py = pIn2; 
 
      /* Decrement the loop counter */ 
      blkCnt--; 
    } 
  } 
  else 
  { 
    /* If the srcBLen is not a multiple of 4,  
     * the blockSize2 loop cannot be unrolled by 4 */ 
    blkCnt = blockSize2; 
 
    while(blkCnt > 0u) 
    { 
      /* Accumulator is made zero for every iteration */ 
      sum = 0; 
 
      /* Loop over srcBLen */ 
      k = srcBLen; 
 
      while(k > 0u) 
      { 
        /* Perform the multiply-accumulate */ 
        sum += ((q31_t) * px++ * *py++); 
 
        /* Decrement the loop counter */ 
        k--; 
      } 
 
      /* Store the result in the accumulator in the destination buffer. */ 
      *pOut = (q15_t) (sum >> 15); 
      /* Destination pointer is updated according to the address modifier, inc */ 
      pOut += inc; 
 
      /* Increment the MAC count */ 
      count++; 
 
      /* Update the inputA and inputB pointers for next MAC calculation */ 
      px = pIn1 + count; 
      py = pIn2; 
 
      /* Decrement the loop counter */ 
      blkCnt--; 
    } 
  } 
 
  /* --------------------------  
   * Initializations of stage3  
   * -------------------------*/ 
 
  /* sum += x[srcALen-srcBLen+1] * y[0] + x[srcALen-srcBLen+2] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]  
   * sum += x[srcALen-srcBLen+2] * y[0] + x[srcALen-srcBLen+3] * y[1] +...+ x[srcALen-1] * y[srcBLen-1]  
   * ....  
   * sum +=  x[srcALen-2] * y[0] + x[srcALen-1] * y[1]  
   * sum +=  x[srcALen-1] * y[0]  
   */ 
 
  /* In this stage the MAC operations are decreased by 1 for every iteration.  
     The count variable holds the number of MAC operations performed */ 
  count = srcBLen - 1u; 
 
  /* Working pointer of inputA */ 
  pSrc1 = (pIn1 + srcALen) - (srcBLen - 1u); 
  px = pSrc1; 
 
  /* Working pointer of inputB */ 
  py = pIn2; 
 
  /* -------------------  
   * Stage3 process  
   * ------------------*/ 
 
  while(blockSize3 > 0u) 
  { 
    /* Accumulator is made zero for every iteration */ 
    sum = 0; 
 
    /* Apply loop unrolling and compute 4 MACs simultaneously. */ 
    k = count >> 2u; 
 
    /* First part of the processing with loop unrolling.  Compute 4 MACs at a time.  
     ** a second loop below computes MACs for the remaining 1 to 3 samples. */ 
    while(k > 0u) 
    { 
      /* Perform the multiply-accumulates */ 
      /* sum += x[srcALen - srcBLen + 4] * y[3] , sum += x[srcALen - srcBLen + 3] * y[2] */ 
      sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum); 
      /* sum += x[srcALen - srcBLen + 2] * y[1] , sum += x[srcALen - srcBLen + 1] * y[0] */ 
      sum = __SMLAD(*__SIMD32(px)++, *__SIMD32(py)++, sum); 
 
      /* Decrement the loop counter */ 
      k--; 
    } 
 
    /* If the count is not a multiple of 4, compute any remaining MACs here.  
     ** No loop unrolling is used. */ 
    k = count % 0x4u; 
 
    while(k > 0u) 
    { 
      /* Perform the multiply-accumulates */ 
      sum = __SMLAD(*px++, *py++, sum); 
 
      /* Decrement the loop counter */ 
      k--; 
    } 
 
    /* Store the result in the accumulator in the destination buffer. */ 
    *pOut = (q15_t) (sum >> 15); 
    /* Destination pointer is updated according to the address modifier, inc */ 
    pOut += inc; 
 
    /* Update the inputA and inputB pointers for next MAC calculation */ 
    px = ++pSrc1; 
    py = pIn2; 
 
    /* Decrement the MAC count */ 
    count--; 
 
    /* Decrement the loop counter */ 
    blockSize3--; 
  } 
 
} 
 
/**  
 * @} end of Corr group  
 */ 
